The present invention relates to a rolled paper holder and a printer incorporating the same.
A printer is known for forming images (including “character printing”) on a recording medium such as paper (hereinafter, referred as “recording paper”), using rolled paper as the recording paper. The rolled paper is advantageous in that it enables a continuous supply of the recording paper for a long time period.
In the printer of this type, there are a shaft-supporting type and a throw-in type in connection with the structure of a paper feeding section for holding the rolled recording paper. In comparison with the shaft-supporting type, which employs such structure that the supporting shaft is inserted into the core hole of the rolled paper, the throw-in type is very convenient since the operation for setting the rolled recording paper is simply to put the rolled recording paper into a paper storage space.
A first example of a related-art throw-in type printer 80 (line thermal printer) will be described below with reference to FIGS. 9 through 13. Incidentally, the overall structure (e.g., a casing body) of the printer 80 will not be shown.
As shown in FIG. 9, the thermal printer 80 comprises a rolled paper holder 71, a thermal recording head 20 disposed on one side (front side of the printer) of a paper storage space 72, and a platen roller 30.
The rolled paper holder 71 includes a curved bottom face 71f for supporting the rolled paper 10 from the lower side, and a right guide face 71d and a left guide face 71g upright from the bottom face 71f. A recess 71k is formed at a center part of the bottom face 71f for holding the rolled paper 10 irrespective of the remaining amount thereof.
The right guide face 71d and the left guide face 71g are configured to face a right end face 10b and a left end face 10c of the rolled paper 10 respectively. The distance between the right guide face 71d and the left guide face 71g is determined to be slightly larger than the width of the rolled paper 10. Therefore, paper 11 drawn out from the outer most periphery of the rolled paper 10 is guided to a recording section including the platen roller 30 and the thermal recording head 20 while being regulated in position at both edges thereof by the right guide face 71d and the left guide face 71g. 
The platen roller 30 is rotatably disposed in parallel with the axial core of the rolled paper 10. The thermal recording head 20 is disposed in parallel to and opposed to the platen roller 30. The thermal recording head 20 is pivotably supported by supporting shafts 20a, 20b provided in parallel with the axial core of the platen roller 30. The thermal recording head 20 is urged by a not-shown resilient member so that the recording face thereof is pressed against the platen roller 30 in the direction indicated by an arrow F1 in FIG. 9.
The rolled portion of the rolled paper 10 is held in the paper storage space 72, and the paper 11 drawn out from the outermost periphery thereof is clamped between the platen roller 30 and the thermal recording head 20. The paper 11 is thus transported in a predetermined direction (the direction indicated by an arrow Y) by the rotation of the platen roller 30 when a not-shown driving source such as a motor is activated.
The printer 80 may be provided with a near-end detector 40 for detecting that the remaining amount of the rolled paper 10 is coming to an end.
The near-end detector 40 includes a frame 44, a contact 41, a spring 43, and a switch 42. The contact 41 is pivotably supported by a supporting member 44a of the frame 44, and the extremity 41a of the contact 41 is pressed by resiliency of the spring 43 so as to come into contact with the left end face 10c of the rolled paper 10.
The switch 42 is operated in accordance with the pivotal position of the contact 41. The switch 42 is set to operate in such a manner that the height of the center of the rolled paper 10 is lowered as the rolled paper 10 is being consumed, and when the remaining amount is below a predetermined amount, the extremity 41a of the contact enters the rolled paper core hole 10a by a force of the spring 43 in the direction indicated by an arrow G and a phantom line shown in FIG. 10. During this operation, the contact 41 is pivoted and activates the switch 42. The near-end state that the remaining amount of the rolled paper is below the predetermined amount is detected by the switch 42.
In such a printer 80, slight variations in parallelism exist between the bottom face 71f of the rolled paper holder 71 and the platen roller 30, and variations occur in the outer diameter of the platen roller 30. When the paper 11 is drawn out from the rolled paper 10, the amount of paper feeding on the left and the right in the widthwise direction of the paper 11 differs from each other due to such variations. As a result, a component force is generated in the direction of the width of the paper, so that the paper 11 shifts in the direction of the width at the portion of the outermost periphery of the rolled paper 10 as shown in FIG. 11.
In such a case, the paper 11 travels in a state where the left end face 10c of the rolled paper 10 is in contact with the left guide face 71g. Therefore, the right end face 10b of the rolled paper 10 is brought into contact with the right guide face 71d on the other side by the reaction force. In addition, when the rolled paper 10 is consumed and the weight is reduced, the influence of the frictional force due to the contact between the right end face 10b of the rolled paper 10 and the right guide face 71d increases. Further, when the frictional force is generated in the hatched section A shown in FIG. 12, the entire rolled paper 10 is lifted by the force B drawing out the paper 11.
Specifically, a moment works as a rotational force to lift the rolled paper 10 in the direction indicated by an arrow C about the position of the hatched area A as a rotation center (here, the rotation radius is represented by L5). Accordingly, the rolled paper 10 is lifted from the bottom face 71f, so that the holding state of the rolled paper 10 becomes unstable. Further, the edges of the paper 11 are strongly brought into contact with the side guide faces 71d, 71g of the rolled paper holder 71. As a result, the paper 11 cannot be accurately fed (skewed travel is occurred), and the edges of the paper 11 are bent. Further, erroneous detection of the near-end detector 40 would occur and noise is generated when the lifted rolled paper 10 returns to the original position thereof and collides with the bottom face 71f. 
As noted, a pressing force of the spring 43 always acts on the contact 41. Therefore, the right end face 10b of the rolled paper 10 is strongly brought into contact with the right guide face 71d in comparison with the case in which the near-end detector 40 is not provided. In other words, frictional force generated in the hatched area A increases, thereby increasing the possibility of the above lifting phenomenon.
A problem arises in that while at least a certain level of spring load is required for the spring 43 in order to secure the accuracy of the near-end detector 40, a smaller spring load is advantageous for preventing the lifting phenomenon of the rolled paper 10, and it was very difficult to achieve a setting which satisfies both conditions.
As shown in FIG. 13, there is a case where the extremity 41a of the contact 41 enters the space between the rolled paper 10 and the bottom face 71f when the rolled paper 10 is lifted.
In such a situation, the near-end detector 40 is activated before the paper reaches the predetermined remaining amount. In addition, it may cause skewed travel of the paper 11 because the rolled paper 10 is obliquely held in the paper storage space 72. Consequently, problems such as misalignment of printing position and bending of the paper edge may occur.
The width of the rolled paper 10 varies from one another due to manufacturing error or the like. Therefore, the storage space 72 width between the left and right guide faces 71d, 71g is set to accommodate the largest possible width of the rolled paper 10. For example, when the smallest possible width of the rolled paper 10 is accommodated in the storage space 72, the rolled paper 10 moves in the widthwise direction thereof due to gaps formed between the side end faces 10b, 10c and the guide faces 71d, 71g. As a result, the positional control of the paper 11 cannot be stabilized, so that deviations of the printing position in the widthwise direction of the paper 11 are generated.
In order to solve this problem, there is a printer in which one of the side guide faces of the rolled paper holder 71 is fixed as a reference side, while the other is provided with a guide member movable in the widthwise direction of the rolled paper 10. However, the movable guide member has to be always brought into contact with the side end face of the rolled paper 10 by the resilient force of a spring member or the like in order to press it against the fixed side guide face of the rolled paper holder 71. To attain stable contact between the rolled paper 10 and the fixed side end face, the resilient force has to be stronger than a certain level. As a result, the possibility of the problems such as the above-described lifting phenomenon is increased.
A second example of a related-art printer 90 will be described with reference to FIGS. 14 through 16. The members similar to those in the first related-art printer 80 will be designated by the same reference numerals, and the repetitive explanation for those will be omitted.
The printer 90 is different from the printer 80 in structure of a rolled paper holder. Specifically, as shown in FIG. 14, a rolled paper holder 91 is configured with the distance L1 between front end portions 91d, 91g of a right guide face and a left guide face adapted to have the same dimension corresponding to the rolled paper 10 in substantially the same manner as in the first related-art printer 80. However, the distance L2 between rear end portions 91e, 91h of the right guide face and the left guide face is adapted to be relatively large with respect to the rolled paper 10. In other words, the distance between the left and right guide faces of the rolled paper holder 91 gradually increases from the front side to the rear side of the printer 90 (from the right side to the left side of FIG. 14).
On the other hand, as shown in FIG. 15, the distance L4 between upper end portions of the guide faces of the rolled paper holder 91 is larger than the distance L3 between lower end portions of the guide faces.
With this arrangement, only the portions of the guide faces that are closer to the front end and a bottom face 91f of the rolled paper holder 91 (i.e., the hatched portion Z in FIG. 16) are brought into contact with the side end faces 10b, 10c of the rolled paper 10. Hence, the portion where the frictional forces are generated between the guide faces of the rolled paper holder 91 and the side faces of the rolled paper 10 opposes the lower part of the rolled paper 10, thereby suppressing the occurrence of the lifting phenomenon. However, the holding stability with respect to the rolled paper 10 lowers at the rear end portions and the upper end portions of the guide faces of the rolled guide holder 91 (i.e., the portions where the distances therebetween are enlarged). Specifically, there is a problem that the amount of inclination of the rolled paper 10 in the widthwise direction thereof increases when the rolled paper 10 having an outer diameter (thickness) relatively larger than the width thereof is initially used. Therefore, the rolled recording paper cannot be held stably.
It is preferable that the position of installation of one single printer is not limited to the horizontal face, but may be selected from a plurality of choices such as the slope face or the vertical wall face in order to increase flexibility of conditions of installation (the place of installation).
The rolled paper 10 can be stably held when the printer 90 is installed on the horizontal face because the distances between the front end portions and the rear end portions of the guide faces of the rolled paper holder 91 are substantially coincident with the width of the rolled paper 10. However, if the printer 90 is installed at such a position that the rolled paper 10 is placed at the rear part of the rolled paper holder 91, stable holding cannot be attained.
Structures similar to the related-art printers are disclosed in Japanese Patent Publication No. 2000-44099A, for example.